Search Documents

By D. U. Deere, F. D. Patton

Introduction A close relationship exists between the geologic investigation and the stability analysis of the slopes of an open pit mine. One significant result of this relationship is that the stability analysis is no better than the assessment of pertinent geologic factors that enter into the analysis. In some slope stability problems the engineering solution becomes obvious once the geologic framework is established. In other cases, establishing the geologic framework is only the first stage in the process of analysis. However, even in these cases the geology should not be neglected once the analysis is made. The geology should be periodically reviewed when new slopes are excavated. This will help ensure that the basic assumptions for the analysis have not changed and will permit changes when new conditions are encountered. In recent years improved methods of stability analysis have been accompanied by advances in laboratory testing techniques and new knowledge of the shear strength of rock discontinuities. At the same time there have been improvements in field geological descriptions. As more experience is gained in analyzing and predicting the stability of rock slopes, the importance of certain geologic factors has become more apparent. Some of these factors were described in a paper given at the Open Pit Mining Symposium in Johannesburg, South Africa in September 1970 (I). This paper includes many of the points covered at that meeting but with additional emphasis on the significance of the major geologic structures. Other papers given at the South African symposium also considered geological and hydrogeological factors in slope stability analysis (2) (3) (4) (5) (6). This paper first describes the approach to a slope stability problem including assessment of the relative roles of field geology studies, laboratory testing, stability analyses, and continued slope monitoring studies. Next, is described a framework which has been found useful for classifying or separating the several types of slope stability problems encountered in open pit mines. The principal geologic factors in slope stability problems in rock are discussed and brief comments are made on how these factors distinguish stability problems in rock slopes from those normally encountered in soil slopes. The over-riding control of major geologic structures, especially faults, in most slope stability problems is emphasized. In this regard the relative importance of statistical studies is contrasted with knowledge of the positions of key structural

Jan 1, 1971

By W. J. Parton

The efficient recovery and preparation of small sizes of anthracite called No. 4 Buckwheat (3/32 by 1/32 in.) and No. 5 Buckwheat (1/32 in. by 0), pre-sent a difficult problem to the anthracite operators. In many instances preparation of these sizes, particularly No. 5 anthracite, is extremely inefficient. In many of the older preparation plants, inadequate facilities, and often none at all, were provided as an integral part of the plant for cleaning this fine anthracite. Consequently, much of the material smaller than 3/32 in. was discarded. As the demand for these sizes increased, facilities for preparing the fine sizes were often crowded into existing structures with consequent sacrifices of capacities and efficiency. In addition to this condition, the methods of preparing the finest sizes are being developed in an attempt to improve their efficiencies. Because the demand for small sizes of anthracite still is increasing, many operators would benefit by investigating and improving the cleaning equipment employed on these sizes. The object of this paper is to de- scribe a stationary screen device from which the underflow is restricted by orifices, called a launder screen, along with operating results of several applications of this screen; a settling tank in which two classified products are produced by the installation of a cylindrical partition of smaller diameter than the original tank, one product being recovered from the small tank created by the partition and one product from the space between the inner and outer tank walls; a small pocket classifier or hydraulic trap for use in removing high ash particles from a sludge flow; the classification or segregation of sludge solids occurring in a 16 in. diam pipe flow by analysis of samples procured at different zones; and the operating results of a Fahrenwald sizer, as well as the performance of the concentrating tables handling the classified products. These simple devices were employed at the collieries of the Lehigh Navigation Coal Company Incorporated, Lansford. Pa., in order to improve preparation results on the fine sizes of anthracite. Launder Screens The launder screen is a screening and dewatering device which probably could be used advantageously in the flow diagram of many fine coal plants. Fig 1 shows that it consists of a stationary screen constructed by placing 6 in. high partitions every 6 in. along a launder. Holes are then drilled on 6-in. centers across the bottom of the launder to receive pipe bushings of the desired diameter. The screen cloth is tacked on top of the partitions. When water and solids are fed to the screen, only a small portion of the total water is removed through the orifices in each compartment so that the water in the feed is distributed evenly over the whole length of the screen. The screening action which results is very efficient because the solids are kept in a fluid condition for the full length of the screen. Blinding of the screen can be minimized by the use of screen cloth

Jan 1, 1950

By F. J. Lecznar

An investigation of the problem of separating two minerals by a moving inclined plane has revealed that only minerals with considerable difference in sliding friction coefficients separate readily; that it is possible to separate two minerals when only one of them has a rolling friction coefficient; that difference in geometrical shape of the minerals is important to separation which improves as grain size increases; and that the thickness of the stream falling on the belt influences the grade of separation - the thinner the stream, the smaller the interference between the grains of the minerals to be separated and the higher the degree of separation. The problem of separating two minerals with different friction coefficients and shapes by a moving inclined plane has been investigated. Friction separators can be used to separate two materials that differ in shape and in friction coefficient. 1,3 Gladkov has presented some theoretical aspects of using a moving plane to clean corn and podded seeds; this method, however, did not result in practical application. When considering the separation of minerals, only those with considerable difference in sliding friction coefficients can be taken into account. Furthermore, it is possible to separate two minerals when only one of them has a rolling friction coefficient. The difference in geometrical shape of two minerals is also important to separation. It has been found that the separation of two minerals improves as the grain size increases. For example, coal and slate over 2 in. in grain size separate much better than materials of smaller grain size. As Table I indicates, the slate grains smaller than 25 mm gradually lose their flat shape with decreases in size and are more rounded than larger grains, which are almost flat. The smallest grains of slate in first and second fractions slide down the belt since their friction coefficients decrease and approach the value of the rolling coefficient. The percentage of separation of the first fraction is, therefore, low. Thickness of the coal stream falling on the belt also influences the grade of separation; the thinner the stream, the smaller the interference between the grains of the two minerals to be separated and the higher the degree of separation.

Jan 1, 1963

By J. G. Mravec

The SO-called gas-tube method as developed by Hare, Peterson and Soler for determining the type and content of gases in molten steel is particularly adapted for determining the hydrogen content in molten steel. The development of this method has been quite completely discussed in a paper published by these co-workers in 1937.' The purpose of this paper, therefore, is to familiarize with this method those who arc not well acquainted with it. The principle of the gas-tube method is as fol1ows: One end of an evacuated gas tube is sealed with a very thin copper disk. when this end of the tube is immersed in a test spoonful of molten steel, the copper disk melts almost immediately, allowing a portion of the steel to be drawn up into the evacuated space. Any dissolved gases, and those produced by reactions between the components of the steel during freezing, are liberated into the unfilled portion of the sampling tube. A blob of steel that forms on the immersed end of the tube after the sample is drawn up seals up the end, making it airtight again. The evolved gases are subsequently drawn out of the gas tube through a suitable valve and analyzed by means of an Orsat apparatus. The volume of the sampling tube is sufficiently large so that a pressure considerably below atmospheric is produced after the gas evolution. The low pressure is necessary to effect a nearly complete removal of gases from the steel. Construction oF Sampling Tube The sampling gas-tube apparatus is illustrated in Fig. I. Seamless S.A.E. tubing used for section A is first cut into 7-ft. lengths. Through cxperiencc it was found necessary to use two sizes of tubing for this part, "is-in. and 3/4-in., respectively. The smaller tubing is generally used on the hotter or lower carbon steels. If the inside wall of the tube A is coated with grease or oil, it should be burned out before being machined as follows: One end is machined on the inside diameter to a depth of 34 in., so as to form a seat for a 7/8-in copper disk, which is stamped out from 0.005 to 0.007-in. thick copper sheet. The other end is machined on the outside diameter to a diameter of 1 5/16 in., to take a small reservoir or trap member I?. About 4 in. below the same end, a 1/2-in. hole is drilled to receive the 1/2-in. copper tubing leading to the large reservoir C. The inside of tube A is then thoroughly cleaned with a round wire brush, such as is generally used to clean out shotgun barrels. It is very important that the surface be absolutely free of rust or any nonmetallic coating. Next, the thin copper disk is soldered in place with low-melting silver solder.

Jan 1, 1945

By Maurice C. Fetzer, Charles R. Austin

It has long been known that plain high-carbon steels may be susceptible to graphiti-zation below the A1 critical, but no data have been available to indicate what factors cause and tend to inhibit graphite formation. Two recent publicationsl,2 have shown that the factors controlling graphitization below the A1 are different from those operating above the A1 inversion where commercial graphitization of malleable iron begins. Furthermore, for plain high-carbon steels graphitization below the critical point does not appear to be related to ordinary chemical analyses. Many years ago it was recorded3 that the rate of graphitization at subeutectoid temperature is not a maximum just below the A1 critical, but at some lower temperature, which Austin and Norris have shown to be about 670°C. Indeed, work done in our laboratory has demonstrated that it is impossible to spheroidize certain steels in the temperature range of 650° to 710°C. without the formation of considerable amounts of graphite. However, if the temperature is maintained just below the A1 (720°C.) these same steels may be completely sphe-roidized at constant temperature. In previous studiesl,2,4 on I per cent plain carbon steels graphitization was encountered during prolonged tempering. The limited number of steels studied did not provide sufficiellt data to permit adequate study of the factors controlling this graphitization. Accordingly, a limited statistical investigation was undertaken, utilizing 18 steels of similar chemical analyses, furnished by four steel companies, who also supplied information regarding the history of manufacture. An extensive program of research is being carried out on these steels, including the effect of pretreatment and atmosphere on the nature and extent of graphitization, and the possible correlation of graphitization with such characteristic properties as hardenability, grain size and mechanical behavior. In the present paper discussion is restricted to a study of the correlation between graphitizing tendency at 670°C. after quenching from several temperatures above the critical, and (I) the minor variations in the chemistry of these steels of "similar" chemical composition, and (2) the deoxida-tion practice employed. The state of the lead bath, oxidized or protected from oxidation by charcoal, used in the tempering treatments is also considered. Materials Eighteen plain carbon steels of about I per cent carbon, and containing similar amounts of each of the other common elements usually found as impurities, were obtained in the form of rods % in, in diameter from four steel manufacturers. The analyses for ordinary and special elements of all the steels were made on the rod stock as received in the laboratory, and the re-

Jan 1, 1941

By E. H. Citron

CLEANING fine coal in jigs is not new in Europe, where the feldspar jig is being used almost exclusively for this purpose. A feldspar jig operates with an artificial bed made up generally of feldspar or other hard rock material. Dimensions and specific gravity of this material must be of suitable values for good bedding qualities. For good efficiency, the size should range between 1x2 in. and 2x2x½ in. thick. The disadvantage of an artificial bed is that it is not mobile and must be replaced every so often with new material to obtain good cleavage characteristics. A semi-mobile bed has been developed to retain only a part of the feldspar on the sieve screen— the other part is drawn off with the refuse material, from which it is reclaimed and returned to the jig feed. Recirculating this feldspar rock offers definite advantages. However, in time it will lose its original shape because of wear, and new bed material must be added to the jig feed. The latest feldspar jigs arc generally air-pulsated, Baum-type jigs, although more than 70 pct of the feldspar jigs operating in Continental Europe are still of the piston type. These jigs are very popular in Europe, but they do require a great deal of time and attention. New Theory to Eliminate Artificial Bedding: At the preparation plants of Pittsburg & Midway Coal Mining Co. it has always been the contention that a small piston-type jig could be developed to clean fine 1/4x0-in. coal down to 28 to 60 mesh efficiently by obtaining and admitting bedding material from the present plant refuse circuit to the jig feed. This eliminates use of artificial bedding materials. The jig should incorporate these essential adjustable features as follows: Adjustable Sieve Screen A screen that can be raised and lowered to increase or decrease washing compartment depth. The sieve screen also can be set on an incline level, or decline. Adjustable Plunger Eccentric Length of stroke can be adjusted to increase or decrease pulsion and suction. Variable Plunger Speed Variable speed reducer for decreasing and increasing the number of strokes per minute. Water Distribution Adjustable baffle plate separating the plunger and sieve compartment so the water can be distributed uniformly over the entire sieve screen area. Refuse Ejector Special unique rubber-type refuse ejector gate operated by air and electrically controlled (as a conventional jig). Automatic Control Conventional float that measures the specific gravity of the coal-water refuse medium in the jig is of the submerged type. The float is mounted on a vertical stem held in position by two parallel arms. A movable weight regulates the effective specific gravity of the float. The float stem can be raised and lowered, having a graduated scale to indicate the depth of bed for the setting of the float. Hutch Drawoff Hutch material is drawn from the cell compartment to the elevator compartment by gravity. The first one-cell experimental jig incorporating all these features was built in January 1955 by Ore

Jan 1, 1959

By Charles A. Anderson

The Bagdad copper deposit is of the disseminated type (porphyry copper) occurring in a quartz monzonite stock of late Cretaceous or early Tertiary age. This stock, located essentially at the intersection of two dike swarms, is the only one of several stocks cropping out in the area which is appreciably fractured and mineralized. Most of the rocks in the area are of pre-Cambrian age, but their structures have had no discernible influence on the copper mineralization. Hypogene alteration of the quartz monzonite includes the addition of quartz, orthoclase, and sericite and recrystalli-zation of biotite. The hypogene sulphides are pyrite, chalcopyrite, and molybdenite, the latter younger than the chalcopyrite. The late Cretaceous or early Tertiary igneous rocks, veins, and faults were controlled by northeast and northwest shear zones, the intersection of which marks the zone of appreciable copper mineralization. The minor mineralized fractures carrying the bulk of the copper have a preferred orientation parallel to the intersecting shears, and it is concluded that they are of tectonic origin rather than the result of shrinkage on cooling, crystallization, or mineralization. Supergene enrichment during late Tertiary or early Pleistocene time formed a chalcocite zone providing the minable copper ore. The enrichment was controlled in large part by northeast and northwest faults, prticularly at their intersection or where the faults are closely spaced. Introduction A major objective in a regional geologic study of a mining district is to determine whether any structural pattern can be found that has a bearing on the control of mineralization. The Bagdad copper deposit is of the disseminated type (porphyry copper) occurring in a.quartz monzonite stock which is located essentially at the intersection of two dike swarms (Fig 2). Of several quartz monzonite stocks in the area only this One is appreciably fractured and mineralized. The origin of the minute mineralized fractures in disseminated copper deposits has long been a challenging problem to the mining geologist, and evidence has been obtained to suggest that the mineralized fractures at Bagdad are related to a regional pattern of conjugate shears which also controlled the location of the dike swarms. The purpose of this paper is to Present this evidence and to emphasize the structural control of the supergene enrichment in forming a chalcocite zone that has provided the ore for the Bagdad mine. The field work on which these conclusions are based was done between October 1943 and August 1945, as a part of the copper investigations of the Goelogical Survey, U. S. Department of the Interior. The writer and his associates, E. A. Scholz and J. D. Strobell, Jr., have prepared a comprehensive report on the geology and ore deposits of the Bagdad area which will be published subsequently by the Geological Survey. Bagdad is located in west-central Arizona in Yavapai County. Ransome' divided the State of Arizona into three provinces: I? the plateau to the northeast; 111, the desert region to the southwest and 11, the moun-

Jan 1, 1949

By J. Wade Watkins, E. S. Mardock

The accurate evaluation of reservoir-performance characteristics in the secondary recovery of petroleum by water flooding requires use of a water tracer that may be injected into water-input wells and detected at oil-production wells to supplement data obtained from core analyses, wellhead tests, and subsurface measurements. Radioactive iodine has been used successfully as a water tracer in field tests to determine: (I) relative rates and patterns of flow of injected water between water-input and oil-production wells and (2) zones of excessive water entry into oil-production wells. Laboratory evaluations of potential water tracers, previous tracer studies, the value of using a radioactive tracer, general field procedures, and the use of surface and subsurface instruments for the detection of the emitted gamma radiation, are summarized. Data from the field tests are presented graphically and discussed in detail. It is concluded that the radioactive-tracer method, using radioactive iodine, may be used successfully to measure either the relative rates and patterns of flow or zones of excessive water entry into wells under conditions of comparatively rapid transit time between wells. INTRODUCTION Extensive use is made of data obtained from core analyses, wellhead tests, fluid characteristics, and subsurface measurements in evaluating the sweep efficiency of water injected into oil sands for the recovery of oil. Theoretical flow rates and patterns may be calculated from those data using radial-flow formulas, if it is assumed that the physical conditions in the productive formation are homogeneous. Unfortunately, homogeneous conditions rarely, if ever, exist in oil-productive formations. The use of a tracer that may be injected into an oil sand and detected quantitatively, or even qualitatively, at offsetting oil-production wells provides basic data that may be used in determining more accurately the subsurface rates and patterns of flow of injected water between wells than is possible by theoretical calculations based on assumed conditions. Consideration of the data obtained by using a water tracer assists in the application of remedial measures to water-input wells, such as plugging of channels, or selective plugging of highly permeable zones, thereby effecting a more uniform flood and a greater ultimate oil recovery. A water tracer should have the following characteristics: (1) low adsorption on solid reservoir material; (2) high solubility in water; (3) low or negligible solubility in crude petroleum; (4) a wide range of solubility of compounds that may be formed by chemical reactions with ions present in reservoir rocks or waters; (5) high detectability in low concentrations by portable apparatus; and (6) general availability at low cost. Additional desirable characteristics are that the tracer should be nonhazardous in nature under normal working conditions and quantitatively detectable in the well bore, as well as at the surface. Review of Previous Tracer Studies The need for a water tracer has been recognized for many years. As far back as 1906, Dole1 described the use of fluorescein in flow-rate studies made in France in 1901. In 1921, Ambrose" discussed in detail the use of organic and inorganic dyes, chlorides, nitrates, and other anions, lithium salts, and the Slichter electrical

Jan 1, 1955

By C. R. King

Most of the acid volcanic glasses such as obsidian, perlite, pitchstone, pumice, and pumicite (volcanic ash) are susceptible to some expansion if suddenly subjected to a suitably high temperature in a properly designed furnace, and subsequently suddenly cooled. Expansion results from the action of chemically combined or dissolved water expanding as a vapor within the softened heated rock particles. This expansion forms countless minute bubbles within the pasty mass of the natural glass particles. If the particles are cooled before these bubbles can escape, the resulting products are cellular, more or less spherulitized glass froths or hollow glass spheres of many types. Chemically, they are essentially aluminum silicates containing about 70 to 75 pct silica, 10 to 16 pct alumina, and 2 to 7 pct sodium plus potassium oxides. They are relatively resistant to attack by acids or alkalies, are resistant to heat up to over 1000°F, and are completely inert to insect or fungus attack. These products are of great potential value in many branches of industry as insulation materials, aggregates, fillers, abrasives, and additives. By proper selection of the perlite rock type and control of processing conditions, expanded perlite of a bulk density varying from about 2 to 20 Ib per cu ft can be • made. The physical properties of the particles comprising a product of a given bulk density also may be varied within wide limits of porosity, water absorption, and crushing strength. In general, crushing strength of expanded perlite increases in direct relation to increase in bulk density, but insulating value varies in inverse ratio to bulk density. The selection of a particular grade of expanded perlite for a given use as an aggregate is therefore always a compromise between insulating value, lightness, and friability. If porosity and water absorption are factors affecting the use of the material, factors other than bulk density are important. Some types of perlite rock tend to decrepitate excessively during expansion, resulting in a highly porous or even hygroscopic product of high friability relative to the bulk density of material produced. In general, treatment of any good perlite rock below the temperature necessary for maximum expansion, or insufficient time in the hot zone of the furnace for effective heat penetration to the core of the rock particles will result in some decrepitation and high porosity in the expanded product. On the other hand, exposure of the material to the temperature required for optimum expansion for a period of time slightly longer than that necessary for proper heat absorption will result in a slightly heavier product of extremely low porosity, i. e., a glazed surface. It is beyond the scope of this paper to describe in detail the rock types and processing methods used to produce the many types of expanded perlite in present use, or that may be produced to fill the present and future needs of industry. A few phases of the economics involved in processing and selling products made from this abundant and cheap mineral raw material, plentifully distributed in large and relatively accessible deposits in most western states and in other areas within economic shipping distance of large centers of consumption, will be treated with particular reference to the Los Angeles area. Relation of Balk Density to Use and Cost of Production Perlite differs from most other lightweight aggregates and fillers in that the raw material (perlite rock) may be quarried much as rock arid sand is mined, and then shipped into consuming areas as crude rock in open gondola cars at correspondingly low freight rates and handling costs. At processing plants in or near large consuming areas the rock is converted into relatively fragile, very bulky products which in most cases are used within a short haul of the processing plant or enter into a manufactured product made at the site of the perlite processing plant.

Jan 1, 1950

By J. C. McCarthy, J. B. Stone

AT Fresnillo a series of veins that has yielded very large quantities of silver and other metals has been developed over a length of 6500 ft. and to a depth of over 3000 ft. In the course of this work striking changes in the mineralogy and metal content of the principal veins have been disclosed and are well illustrated by assay data and ore reserve calculations. This paper describes those changes and suggests their bearing on theories of ore deposition. LOCATION The Fresnillo mines and the adjacent city of Fresnillo are in the central part of the state of Zacatecas, 35 miles northwest of the capitol city of Zacatecas, once a great silver-mining center whose total production is said to place it fourth in the world. Another famous old silver district, Sombrerete, lies northwest of Fresnillo. Fresnillo is connected by a 5-mile branch with Fresnillo station on the Mexican National Railways line from Juarez to Mexico City. Lying near the southwestern edge of the central plateau of Mexico, Fresnillo is surrounded by a semi-arid rolling plain from which rise widely scattered low hills. One of these is Proano hill, an inconspicuous elevation rising barely 300 ft. above the plain, but in and around Proa[n]o hill are the Fresnillo mines, and it is marked now by a great gash cut by gloryhole mining. HISTORY According to an account written in 1834 by Francisco García, then Governor of the state of Zacatecas, Fresnillo was discovered in 1554, and a presidio was established there in 1568 to protect travelers on the road between Zacatecas and Sombrerete. Little is known of the earliest mining at Fresnillo. which seemingly began soon after its discovery, but by piecing together various accounts, it appears that mines there were working in 1717 and were notable active in 1751 under an administrator named Murguía, who left detailed notes describing them. In 1757, however, the mines became inactive because of difficulties with creditors and no doubt also because of increasing water troubles, and they remained abandoned until 1830. In 1830 the mines at Fresnillo became the property of the State of Zacatecas because the interest of Governor García had been aroused by the long disregarded notes of Murguía. Under Garcia's energetic leadership the mines were reopened, and silver production began in 1832 in spite of serious difficulties, including abnormal rains and an epidemic of cholera. In 1833 English capital was sought to allow installation of steam-driven Cornish pumps at the two principal shafts and to build the great hacienda de benefacio (the present Proano hacienda). The company formed in 1835 (Cia. Zacatecano-Mexicana) operated successfully until 1872, when its career was brought to an end by the political and economic disturbances

Jan 1, 1942

By Jay R. Burns

Two magnesium sand-casting alloys are commonly favored in the United States. These are referred to as H and C alloys (Dow Chemical Co.) or AM265 and AM260 alloys (American Magnesium Corporation). Both are of an aluminum-zinc-manganese type. H alloy contains 6 per cent aluminum and 3 per cent zinc and is characterized by relatively good toughness. C alloy contains g per cent aluminum and 2 per cent zinc and is employed where high yield strength and pressure tightness are required. Examination of magnesium castings poured in Europe and England,1,2 however, demonstrates that H and C alloys are replaced by A8 and AZ91, respectively. That is, A8 represents a magnesium alloy having superior toughness while AZ91 is suitable for high yield strength and pressure-tight applications. The basic difference between the American and European alloys is that the foreign alloys employ a somewhat higher aluminum content and less zinc than is found in H and C alloys. The mechanical properties of the alloys, when divided into high and low-aluminum groups, are quite similar, as determined from separately cast foundry-control type test bars.3 In this paper the decrease of mechanical properties caused by any given amount of microporosity is measured for H, C, A8, and AZ91 alloys. The relative susceptibility of each of the four alloys to microporosity is also determined. Typical mechanical properties and nominal chemical analyses are reported in Table I. [ ] The apparent similarities between the two alloys in each group have led to considerable discussion as to the relative merits of each of the compositions.2 Popular points for comparison between the alloys have been the relative susceptibility of each of the four alloys to microporosity5 and the effect of this microporosity on their mechanical properties. It is primarily intended, in this paper, to show the

Jan 1, 1946

By d&apos, D. L. Guernsey, J. C. Entremont, John Chipman

The reaction of aluminum with oxygen in liquid iron has been studied at 1740° and 1910°C. Interaction coefficients are very much smaller than those previously published. The equilibrium constant falls within the approximate range of earlier experiments and calculations. It is now well established that the "deoxidation constant" for aluminum in liquid steel at normal steelmaking temperatures is extremely srnall. Thus at 1600 the product [% Al] is of the order of 10- 14. At this temperature, therefore, great experimental difficulties are encountered in any attempt to obtain a direct measure of the constant. If the aluminum content of the metal is high enough to permit accurate analytical determination, that of the oxygen is too low. If the oxygen content is high, the aluminum is below the limits of detection. Our best values of the constant have come, therefore, from indirect calculations or by extrapolation downward from observations at higher temperatures.. For their studies in the range 1695° to 1866°C, Gokcen and chipman' restricted their aluminum concentrations to less than 0.06 pct. Oxygen analyses were made by the vacuum fusion method which appears to be dependable at these low aluminum concentrations. Experimental results, even at the highest temperature employed, are extremely sensitive to small errors in the analysis of either element. The slight change in the equilibrium constant with aluminum and oxygen concentration was utilized in the calculation of interaction coefficients expressing the effect of aluminum on the activity coefficient of oxygen and the reciprocal effect of oxygen on the activity coefficient of aluminum. The range of concentration, however, was so limited that only a rough value for the interaction coefficient could be obtained. This value was much more negative than that found for any other pair of reactants. In view of the very limited range of concentration employed, the reported values have always been regarded as very questionable. A redetermination was the object of the work reported here. EXPERIMENTAL METHOD At high aluminum concentrations, the vacuum fusion method is susceptible to grave error due to absorption of gas by aluminum distilled from the sample. Since it was desirable to extend the study to at least as much as 1 pct Al, another method for analysis was sought. In steels containing more than a few hundredths of a percent aluminum and no other deoxidizing element, it is safe to assume that

Jan 1, 1963

By Peter M. Fozzard

The San Bartolomt silver deposit was discovered by a United Nations team of geologists working with a counter- part team of staff of the Ecuadorian Government's General Directorate of Geology and Mines (DGGM). The Phase I project over five areas of operation during which this discovery was made was financed through a United Nations Development Program contribution of $860,000 and an Ecuadorian Government participation of about $680,000 equivalent. Existence of mineralization at San Bartolomé was first recognized in 1966 when a reconnaissance geochemical stream-sediment program was carried out over a 10 500 km2 (4,054 sq mile) area centered around the city of Cuenca in southern Ecuador. Over the course of this project more than 10,000 samples of stream-sediment, soil, and rock materials were collected. Average costs per sample were $10.00, as follows: collection, $5; sample preparation, $1.60; assay work, $3.40. Initially in the program (1965-1966) sediments were collected along all motorable roads and tracks. Routine analyses, originally by colorimetry and later by AAS, were for Cu, Pb, Zn and occasionally As, Ni, and Co. Discovery geochemical samples from the San Bartolomé drainage area were among the first to be taken in 1965. As luck would have it, the road along which this traverse was taken passes only some 100 m (328 ft) downstream from the mineralized suboutcrop. The relevant two streams sampled are of inconsequential size, some 1 m (3.3 ft) in width, with a limited flow volume throughout the year. Original anomalies were recognized through cold-extractable Cu/Zn analyses. The pH of all river waters was also recorded at sample sites. Resampling the discovery sediments when AAS became available showed total extractable values of between 150 ppm-300 ppm Zn, 550 ppm Pb, and 10 ppm Ag. In 1967 the first followup was by rough-and-ready means. Dithizone field-kits (THM) were used to rapidly test soils from the surrounding area. The area has no outcrop. This work allowed the definition of an area of interest of some 2 km (1.2 miles) x 500 m (1640 ft). Six approximately 1 km (0.6 mile) to 1.5 km (0.9 miles) lines spaced at approximate 250 m (820 ft) intervals were established and used for IP surveys and soil sampling at 50 m (164 ft) intervals. Where one of the lines crossed the westernmost geochemical discovery creek a first-priority geophysical anomaly coincided with a major Zn/Pb (and later Ag) soil anomaly. A pit was sunk and encountered mineralized vein material at a depth of 1.5 m (5 ft). This lucky glory hole confirmed the geochemical discovery and prompted systematic followup. Immediately, costeaning of the west bank of the discovery creek, the Quebrada Ocashuaico, was carried out and exposed weathered and leached mineralization. Nearly 100 mineralized veinlets ranging in thickness from 0.5 cm (0.2 in.) to 8 cm (3 in.) were exposed across the 180 m (59 1 ft) costean. Sixty mineralized veinlets were determined over a 90 m (295 ft) wide zone. Sampling delineated minable widths averaging between 0.16 and 0.31 kg/t (5 and 10 oz per st) Ag with associated copper (very sporadic) lead and zinc. Over the period 1968- 1972 a considerable amount of detailed work was completed: detailed IP, EM Turam, magnetic and mise-a-la-masse geophysics, very detailed soil- sampling, trenching, drilling and glory-hole drifting, and cross-cutting. Numerous problems were encountered: the area was found to be a most difficult geoelectrical target; zero outcrop; pyrite (nonargentiferous zones) associated with faulting; mineralized groundwater; extensive clay development; loss of diamond drill-core, and no two-dimensional surface information. As the program developed the complexity of the structure was slowly unravelled, using a degree of good guesswork. Apart from photogeological and ground geological mapping at various scales, the following

Jan 1, 1985

By Jan H. Hommen

TRENDS IN MINE FINANCE Reviewing historical trends may help in dealing with future funding strategies. The first trend is the increase in the use of debt to fund corporate America. Surprisingly, when comparing that with other corporates in the global marketplace, the U.S. does not look too poorly. Japanese, in particular, but also German companies, are much more leveraged than their U.S. counterparts. Note that in Japan and Germany the government and the consumer have shown substantial restraints when it comes to credit. Not so in the U.S. where the savings rate (4%) is much lower than that in Japan (20%) and in Germany (14%). As a result, the cost of leverage is substantially lower in Japan and in Germany than in the U.S. Lower debt costs in these countries allows one to obtain more of it for the same price. The close relationships between financial institutions, corporations and governments in Japan and Germany also make the risk of leverage more bearable and understandable. Also note that interest rate volatility in these countries is more subdued. The investor base in common stock is also changing. Private pension funds have been net sellers of equities during the last few years while public pension funds have been net buyers. Individuals are basically out of the market. It is estimated that over $330 billion of equity was retired in the U.S. through 1986-1988. The reasons are well known: restructurings, buy-backs, takeovers, mergers, and buy-outs. This de-equitization is likely to continue as the cost of equity capital is higher than the cost of debt capital, even on a before-tax basis. Because there has been no market for equity since October 19, 1987, junk bonds have replaced equity capital in the corporate finance structure. The non-investor-grade borrower has access to the public markets through high-yielding debt securities that often look like senior equity. Deregulation has also provided 24-hour markets; securitization can now liquify assets that before were rusting on balance sheets; information processing and communication tools give facts that are instantaneously available, creating the need for products to cover risk and exposures unknown before the start of the information and technology explosion. Thus we now have swaps, options, futures, options on futures, caps, as well as program trading, portfolio insurance, index funds, etc. Globalization will be unstoppable. Today's environment demands it. Corporations are now global competitors, even though they may have never shipped a product off-shore. Boundaries are disappearing and impediments have been removed. Stocks can be issued in a global offering with distribution in all major financial centers of the world. The high leverage of Japanese companies has made common stocks very scarce, which with the high savings rate, makes equity capital inexpensive in Japan. If markets were perfect everyone would issue stock in Tokyo and buy it back in New York. This would certainly stop the bleeding on the balance of payments. With the deficit balance of payments in America, it is no surprise that the cost of money is expensive here. The risk-return relationship on U.S. equity is not favorable enough to appeal to Japanese equity investors. The Tokyo-market, helped by a stronger yen, surpassed New York as the most important equity market in the world. The question is, will the Tokyo market hold up when Japanese domestic consumption increases at the expense of savings? In the U.S. debt markets, the plain vanilla debenture is making a comeback after a period of absence. Commercial paper has replaced short term bank borrowings for working capital funding by larger corporations. The banks have made an interesting comeback with loan sale programs that will continue to attract borrowers. There will be a continuing

Jan 1, 1990

By L. D. Fetterolf, G. T. Mahler, W. M. Peirce, R. K. Waring

Until recently, the only commercial method of producing magnesium has been fused salt electrolysis, despite a considerable amount of experimental work on the direct reduction of magnesium oxide. In this early work, a number of investigators demonstrated that magnesium oxide would react with any one of several reducing agents to produce magnesium vapor, but that the mixture of magnesium oxide and reducing agent must be heated to a high temperature even in a vacuum. In particular, it was demonstrated that silicon and aluminum are effective reducing agents and that when either of these is used the magnesium vapor can be condensed to massive metal. In spite of this knowledge, no successful commercial reduction process was developed, at least in this country, because of the operational difficulties imposed by the requirement of high temperature and vacuum and because of the high cost of the reducing agent. The outstanding experimental work done by Pidgeon, who carefully reviewed all of the known methods of making magnesium and then selected ferrosilicon reduction, overcame some of the operational difficulties. The process developed by Pidgeon comprises briquetting a mixture of calcined dolomite and reducing agent, preheating the briquets to about 600°C. in an externally heated alloy retort, reducing the MgO with silicon in an evacuated horizontal alloy retort heated externally to about II50 C., and condensing the magnesium vapor to a solid in a cold extension of the retort projecting beyond the front of the furnace. A major advantage of Pidgeon's process is that the retort is not cooled down between charges. Earlier investigators had used apparatus that necessitated cooling and reheating of the retort between charges. Early in January 1942, when the War Production Board was considering the Pidgeon process for quickly increasing the production of magnesium, The New Jersey Zinc Co. offered to have a research investigation of the process carried on, with the hope of assisting in its further development. This offer was accepted, and a two-retort pilot plant was built at Palmerton and put in operation on Jan. 29,1942. An intensive investigation of certain phases of the process was carried out in the ensuing four months. This investigation was completed in the last part of May 1942) and the pilot plant was then shut down. Subsequently, The New Jersey Zinc Co. was requested to have further development work done on the process, and a more extensive investigation was undertaken in August 1942 under contract with the War Production Board and under the supervision of the War Metallurgy Committee. This paper describes the ,phases of the investigation that are thought to be of sufficient general interest to merit publication.

Jan 1, 1944

By W. A. Backofen, G. Mayer

Single crystals of iron, copper, and a Cu-7 wt pct A1 alloy were pulled through conical dies to simulate the constraint in a polycrystalline aggregate undergoing axisymmetric reduction. With Taylor-type hardening, dependence of the drawing stress, od, on the Taylor orientation factor, M, is predictable from the polycrystal stress-strain curve; in particular, for a power-law relationship, it should follow that d log od/d log M = (1 + n). A first-order agreement with analysis was found in the data from iron. For copper, the implied n from the observed d log od/d l°g M was -0, while for Cu-7Al it was negative. The trend was in the direction of random polycrystal behavior. Thus the idea of hardening only in response to the amount of prior slip loses validity as stacking fault energy (SFE) is lowered. Two possible explanations have been suggested: as stacking fault ribbons are widened, barriers from dislocation reactions become increasingly effective in dispersing slip and reducing the orientation dependence of the total glide strain dm that appears in alternatively, or conjointly, the polyslip shear stress, 7, acquires an orientation dependence of a kind which has the same leveling effect on M. The problem of relating the strain hardening of polycrystalline material to that of an isolated single crystal is still largely unsolved. In a new experimental approach from recent work, single crystals of different orientations have been deformed under the constraints found in an aggregate while measuring their deformation resistance. Procedures have involved drawing cylindrical crystals through conical dies1 and compressing slab-shaped crystals in plane strain.2'3 Predictions for the outcome of such experiments were made first by Taylor~ and later, in more general form, by Bishop and Hill.5'6 Taylor's example was the axisymmetric extension of an fcc crystal slipping on the usual {111}(110) systems or, equivalently, a bcc crystal undergoing 'kestricted" slip on {110}(111). In his solution, the deformation work supplied was equated to that dissipated internally in slip on all active systems. With o the single applied tensile stress, dc the resulting axial strain, and dyT the total glide strain on systems operating at resolved shear stress, 7: The orientation dependence of M was found by minimizing dyT for each orientation while activating five independent systems, Fig. l(a).? The Bishop and Hill analysis, based on a principle of maximum work, leads to essentially the same conclusion; the need for at least five active systems is recognized in the finding that either six or eight are actually brought into operation. The mean value from the entire stereo-graphic triangle in either case is M - 3.06. More recently, Hutchinson8 made a Taylor-type analysis for pencil glide in a bcc structure, from which piehlerg prepared Fig. l(b) as the counterpart in Fig. l(a); here M = 2.75. The obvious weakness in such analyses is the indifference to slip-system interactions. A condition of what might be termed "independent"

Jan 1, 1969

By Edward B. Hughes, Frank G. Norris

OXIDATION is characteristic of all processes for making steel from pig iron. This thought has been aptly expressed by H. W. Graham13 in the most recent Howe Memorial Lecture, "The process of steel-making consists of using iron oxide to reduce the carbon content of the pig iron to the desired level." Direct oxidation refers to the reaction that results from introducing oxygen either alone or mixed with other gases directly into the steel bath. In working a heat, oxygen in some form is added to the steel to remove the undesirable constituents as oxides. There are two general methods of supplying this oxygen to the open hearth bath. The method in which the oxygen is added as a, compound such as C02-or iron ore is designated an indirect method because the steel bath must first decompose the compound to attain oxygen in a usable form. The other method in which oxygen is added to the bath in the elemental or gaseous form, more or less diluted by other gases such as nitrogen, is a direct, method because no decomposition is necessary before the oxygen reacts with iron to form FeO which is dissolved in the bath in a usable form. Bubble formation (at least of a macroscopic size) presents no problem in case of direct oxidation because the reacting agent (oxygen) is in the form of bubbles when entering the metal. Regardless of whether oxygen is introduced into the bath directly or indirectly, several reactions proceed concurrently. In the presence of the bath of molten iron, FeO is formed either by oxidation of iron by oxygen or reduction of oxides by iron. This FeO dissolved in the molten iron is the source of oxygen for the oxidation of manganese, carbon, silicon, and phosphorus if these are present. The oxidation of carbon from steel is the controlling steelmaking reaction. The introduction of oxygen into the bath, its reaction in the elimination of impurities, and its control by the use of de-oxidizing additions have been subjects of importance since steel was first made by the bessemer process. Direct oxidation is, in a sense, an application of the bessemer principle to the open hearth process. Graham13 states: "The use of oxygen or air jets introduced into the metal bath is essentially an effort to approach in the open hearth the turbulence, rapid interface reaction, and high production rate per hour that exists in the bessemer process." The general subject, "Oxygen in Steelmaking," was given new life by the studies of Herty and associates starting about1925. The current interest in elemental oxygen is intimately related to the large scale production of oxygen developed during the war period. Some of the first applications were made during the early summer of 1946 at the Steel Co. of Canada using oxygen with the fuel. Such a use is of considerable interest and importance in contributing to faster heats but is not the subject of the present discussion which deals entirely with the introduction of elemental oxygen directly into the open hearth bath. A recent article12 reviewing the current

Jan 1, 1948

By J. L. Carne

ORE control is a matter of planning and supervision based on a foreknowledge of the content and distribution of ore. The Inspiration orebody is predominately a copper-sulphide blanket, overlain by an oxidized zone of copper silicates, copper carbonates, and barren capping. Most of the ore is treated by leaching, and the optimum requirement of this method is the goal toward which the mining schedule is aimed. Both open-pit operations and underground mining are used. The problems of ore control at Inspiration are: I—maintenance of metallurgical balance, 2—conservation of oxide ore, and 3—mining out of the orebody at an average grade which parallels that of the reserve figure. Prior to the fall of 1926 all of the Inspiration division ores were treated by flotation, but the mixed ores of the Live Oak—Keystone section carried too large a proportion of copper in the form of chrysocolla for satisfactory flotation. For this type of mixed ore the leaching process now in use had been worked out, and the plant was put into operation in the fall of 1926. The process is known as the ferric sulphate leach, and the leaching solvents contain both ferric sulphate and free sulphuric acid. Sulphide copper in the form of chalcocite is leached by the ferric sulphate, and the oxidized copper minerals are dissolved by the sulphuric acid. From the beginning of operations to the present time the plant has treated some 67 thousand tons of ore having an average copper content of 1.142 pct, of which 0.605 pct has been in the form of oxidized copper minerals. The plant is currently being operated at the rate of 11,500 tons per day, 7 days per week. However, this tonnage is produced in 6 days of mine operation. The average current grade is approximately 1 pct copper, of which about 50 pct is present as oxidized or acid-soluble copper. Close control of metallurgical procedures is a vital factor in operation of the plant and is in turn dependent upon careful regulation of feed. An excess of sulphide copper requires the presence of more ferric sulphate in the leaching solvents. On the other hand, an excess of ferric sulphate in the presence of a low sulphide feed seriously reduces the efficiency of electrolytic precipitation in tank house operations. This condition must be avoided at all costs. An additional factor must be considered. It is known that the sulphide content is predominant in the ore which remains in the reserve. To maintain the necessary sulphide-oxide proportion, so that the entire reserve will mine out at both a grade and a sulphide-oxide ratio that will be permissible throughout the remaining life of the property, it is obvious that the oxide reserve must be currently preserved to as great an extent as possible. Fortunately much of the oxide reserve is found in the open-pit operation. This happy circumstance adds flexibility to the procedure and makes it possible to maintain the close regulation necessary to insure best overall results, both mining and metallurgical. The two ore streams from the pit and underground operations join at the coarse-crushing plant, and proper control must be exercised before the ore reaches this point. The open pit is currently providing about 55 pct of the ore and underground operations the balance of production. Both operations are under a single superintendent so that the closely interrelated problems may be more readily controlled. The least flexible of the two producing units is the underground mine, where the mining method is block caving. Although a block of ground may be undercut and developed, characteristics of the material determine its caving action. The ore in the chutes must be drawn. The area currently mined from underground is in a zone predominately sulphide and is generally

Jan 1, 1953

By M. B. Bever, A. B. Michael

THE structure of cast A1-Si alloys is altered profoundly by modifying agents. Sodium, in particular, reduces the size of the silicon particles in the eutectic and tends to change their shapes from plates to nearly rounded grains. This refinement is accompanied by a shift of the eutectic to higher silicon concentrations and lower temperatures. Similar effects can be attained by rapid solidification. Hypotheses advanced to explain modification have involved the formation of a ternary eutectic,1 the removal of oxides by fluxing,' and even a presumed allotropic transformation of silicon. Other hypotheses assume that the modifying agent causes an envelopment of the silicon particles by the aluminum-rich solid solution, but attribute this envelopment to different mechanisms. According to various explanations, the growth of the silicon particles is obstructed by an immiscible sodium-rich liquid," an adsorbed layer of sodium,' or a ternary compound;5 his obstruction has been conceived as purely mechanical or as a colloidal action.' It has also been proposed that sodium reduces the surface tension on the Al-Si interface, thus permitting the aluminum-rich solid to grow faster and to envelop the silicon particles.? Still other hypotheses stress undercooling and the attendant change in the rate of nucleation of silicon, but fail to ascribe any definite function to the sodium addition." '" Procedure High-purity alloys of aluminum and 3 or 7 pct Si were treated with modifying agents containing radioactive sodium tracers. The experiments were intended to investigate the partition of sodium between the primary aluminum-rich solution and the eutectic, and, if possible, to determine whether sodium is concentrated in or around the silicon particles in the eutectic. Radioactive sodium fluoride, alone or mixed with stable sodium chloride, was allowed to react with the alloy for 5 min immediately before solidification in the crucible. Modification could not be attained with additions of less than the equivalent of approximately 0.1 pct Na. Some alloys were not completely modified, but comparison of the structures of treated and untreated specimens indicated a very considerable reduction in particle size of the silicon in all of the former. A treated alloy is shown in Fig. 1. Radioactive sodium fluoride was prepared by bombardment with deuterons having an energy of 14 mev. This bombardment (totaling, for example, 6 microampere-hours in one run) produced radioactive Na24 (half-life 14.8 hr) by the reaction 11Na23 (d,p) 11Na24. The radioisotopes of fluorine also produced have short half-lives and were not detected. A half-life determination by counting confirmed that the measured activity was due to Na24. The distribution of the sodium in the solidified alloys was determined by an autoradiographic technique by which a suitable stripping film is attached to a very thin metallographic specimen. After exposure and development, this emulsion remains superimposed on the specimen and may be examined microscopically or photographed by reflected light. The emulsion of the autoradiograph can be correlated directly with the underlying surface by simple adjustment in focus. The details of this technique have been described elsewhere." Results Fig. 2 is a micrograph of the autoradiographic emulsion ("autoradiograph") lying directly above the area of eutectic in Fig. 1. Fig. 3 shows a similar autoradiograph of a region consisting of primary solid solution. The small black dots (tracks) in these autoradiographs are developed grains in the emul-

Jan 1, 1954

By W. A. Tiller, J. P. McHugh

HE majority of liquidus and solidus surfaces in phase diagrams have been determined by the conventional cooling- and heating-curve techniques.' These techniques have two main shortcomings: 1) the solidus may be in considerable error due to the difficulty involved in completely homogenizing the solid and 2) the determination of liquidus and solidus in more than a two-component system does not enable one to determine tie-lines connecting the specific equilibrium solid and liquid compositions. However, in a recent paper by one of the authors,' a method was suggested whereby the liquidus and solidus surfaces plus tie-lines in an n-component system may be determined. This method utilizes a controlled solidification technique and assumes that interface equilibrium exists during freezing. The present work was undertaken with a twofold purpose; first, to determine the liquidus and solidus lines in the pseudo-binary system Bi2Te3-Bi2Se3 by heating- and cooling-curve techniques and, second, to determine the partition coefficients of Te and Se in the BizTe3-,Sex system by controlled solidifica- tion techniques. The two sets of results can be compared to test the accuracy of the controlled solidification method. EXPERIMENTAL I—The starting materials for this study were 997999 pct Bi, Te, and Se, obtained from the American Smelting and Refining Co. The compounds BizTe, and Bi2Se3 were each prepared by melting together stoichiometric amounts of the elements, followed by twelve zone-refining passes. This produced homogeneous bars of the compounds for use in the phase-diagram studies. The apparatus used to obtain heating and cooling curves is illustrated schematically in Fig. 1. The alloy samples were located in a graphite crucible placed in a stainless steel canister. The canister was supported in a heavily lagged pit furnace by a device which oscillated the canister about its vertical axis at a frequency of about 3 cycles per sec during heating and cooling-curve runs. The graphite crucible was designed to minimize the thermal coupling of the sample to the furnace. A thin graphite sleeve separated the alloy sample from the stainless steel tube that housed the thermo-

Jan 1, 1960